jason@gunther:~$ sudo cfdisk -P s /dev/hda
Partition Table for /dev/hda

               First       Last
 # Type       Sector      Sector   Offset    Length   Filesystem Type (ID) Flag
-- ------- ----------- ----------- ------ ----------- -------------------- ----
 1 Primary           0    23438834     63    23438835 Linux (83)           None
 2 Primary    23438835    25398764      0     1959930 Extended (05)        None
 5 Logical    23438835    25398764     63     1959930 Linux swap / So (82) None
 3 Primary    25398765   234436544      0   209037780 Linux (83)           None
jason@gunther:~$ su -
Password:
gunther:~# mkfs
mkfs         mkfs.cramfs  mkfs.ext2    mkfs.ext3    mkfs.minix
gunther:~# mkfs.ext3 /dev/hda3
mke2fs 1.40-WIP (14-Nov-2006)
Could not stat /dev/hda3 --- No such file or directory

The device apparently does not exist; did you specify it correctly?